Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. Cooling water is required for following equipment in ammonia absorption plant

Evaporator

Absorber

Condenser, absorber and separator (rectifier)

Condenser

2. In a refrigeration system, heat absorbed in comparison to heat rejected is

Less

Same

More for small capacity and less for high capacity

3. The operating pressure for refrigerating units using R-12 as a refrigerant is

15 bar

2 bar

8 bar

30 bar

4. The boiling point of ammonia is

-10.5°C

-77.7°C

-33.3°C

-30°C

5. The freezing point of sulphur dioxide is

-135.8°C

-75.2°C

-56.6°C

-77.7°C

6. The condition of refrigerant after passing through the condenser in a vapour compression system is

Dry saturated vapour

Superheated vapour

Saturated liquid

Wet vapour

7. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Sub-cooling or under-cooling

Super-cooling

Normal cooling

None of these

8. Most thermostatic expansion valves are set for a superheat of

5°C

15°C

10°C

20°C

9. Which of the following cycles uses air as the refrigerant?

Ericson

Bell Coleman

Stirling

Carnot

10. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.6

0.4

0.67

0.376

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11. In a lithium bromide absorption refrigeration system

None of these

Ammonia is used as a refrigerant and lithium bromide as an absorbent

Lithium bromide is used as a refrigerant and water as an absorbent

Water is used as a refrigerant and lithium bromide as an absorbent

12. The capillary tube, as an expansion device, is used in

Water coolers

Domestic refrigerators

All of these

Room air conditioners

13. The minimum temperature to which water can be cooled in a cooling tower is

Wet bulb temperature of air

Dew point temperature of air

Ambient air temperature

Dry bulb temperature of air

14. The domestic refrigerator uses following type of compressor

Piston type reciprocating

Centrifugal

Axial

Miniature sealed unit

15. A thermostatic expansion valve in a refrigeration system

Ensures the evaporator completely filled with refrigerant of the load

None of the above

Maintains different temperatures in evaporator in proportion to load

Is suitable only for constant load systems

16. In a refrigeration system, the expansion device is connected between the

Condenser and receiver

Receiver and evaporator

Compressor and condenser

Evaporator and compressor

17. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Brine

Ammonia

Freon

Carbon dioxide

18. The vapour compression refrigerator employs the following cycle

Carnot

Reversed Rankine

Rankine

Reversed Carnot

19. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Equally

Unpredictable

Less

20. Which of the following statement is correct?

(D) Both (A) and (B)

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(B) The increase in air movement increases the evaporation from the human body.

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21. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

1.2

0.2

22. Rating of a domestic refrigerator is of the order of

5 tons

40 tons

0.1 ton

10 tons

23. Critical temperature is the temperature above which

A gas will never liquefy

Water will never evaporate

Water will evaporate

A gas will immediately liquefy

24. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

(T₁ - T₂)/T₁

T₁ / (T₂ - T₁)

(T₂ - T₁)/T₁

T₂/ (T₂ - T₁)

25. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 1

1: 9

1: 3

9: 1

26. The value of C.O.P in vapour compression cycle is usually

Always more than unity

Equal to unity

Always less than unity

Any one of the above

27. Highest temperature encountered in refrigeration cycle should be

Near critical temperature of refrigerant

Above critical temperature

Much below critical temperature

At critical Temperature

28. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

4.33

3.33

1.33

2.33

29. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(A) Heat dissipated to the surroundings

(B) Heat stored in the human body

(D) Difference of (A) and (B)

30. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant temperature

Involves no change in volume

Takes place at constant pressure

Takes place at constant entropy

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31. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

32. A bootstrap air cooling system has

Two heat exchangers

Three heat exchangers

Four heat exchangers

One heat exchanger

33. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Collect vapours

Superheat the vapour

Detect liquid in vapour

Collect liquid refrigerant and prevent it from going to compressor

34. For obtaining high COP, the pressure range of compressor should be

Low

High

Any value

Optimum

35. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Zero

Positive

Negative

None of these

36. Freon group of refrigerants are

Nontoxic and non-inflammable

Non-inflammable and toxic

Toxic

Inflammable

37. The bank of tubes at the back of domestic refrigerator is

Condenser tubes

Capillary tubes

Refrigerant cooling tubes

Evaporator tubes

38. The curved lines on a psychrometric chart indicates

Relative humidity

Dew point temperature

Dry bulb temperature

Wet bulb temperature

39. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

5.12

1.25

2.15

40. Which of the following is not a desirable property of a refrigerant?

High risibility with oil

Low boiling point

Large latent heat

Good electrical conductor

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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